Brake



BRAKE Filed May 6, 1952* 4 Smeets-sheet l 1| 74 L 4s 96 l I 0 86 9675 8266 90 f 72 *fn l Z 87 a 92 50 89 84 INVENToRs Elias/ve G. Carano/.Lxfm,V ROY .nnforaa xpri 20, i937. R s, SANFORD ET AL 2,678,209

INVENToRS EUGENE G. CaeeoLL. Eoy 5. Jefa/vree@ April 2o, 1937. R,SANFORD ET AL 2,078,209

BRAKE Filed May 6, 1932 4 Sheets-Sheet 3 n n n n J MU u u u u /V /V 244SLB 364 l a/g 322 320 Z 5. a/s

' f 476 Sti I\\\\il\\` Z .fao 470 IN VEN TOR-5.

EUGENE G. Cneeou. @o y Jn/wfoeo ATToRNEx .April 20, 1937. R. s. SANFORDyET A1. 2,078,209

BRAKE Filed May 6, 1932 4 Sheets-Sheet 4 CVR ` INVENToRs.

fact/vf' 6I Caeeob Boy Sn/vroeo Patented Apr. 2o, 1937` l 2,078,209

UNITED STATES PATENT OFFICE BRAKE Roy S. Sanford and Eugene G. Carroll,South Bend, Ind., assignors to Bendix Aviation Corporation, South Bend,Ind., a corporation of Delaware Application May 6, 1932, Serial No.609,716 I 21 Claims. (Cl. lss-452) This invention relates to brakes forautomotive sponsive to the initial movement of the pedal vehicles and isdescribed particularly as applied for energizing 8 power dCVCC- to ahydraulic braking system. One of the novel features of our invention isa Service brakes of automotive vehicles are master cylinder providedWith iuid Pressure dC- usually applied through a foot pedal whichnortuating means comprising a chamber adapted to mally throughmechanical or hydraulic linkage receive uid pressure. takes up the slackin the system, applies the A further feature ls the provision of apresbrake shoes to the brake drums, and exerts pressure relief chamberin combination with a master surev to force the shoes more tightlyagainst the cylinder.

10 drums. As the shoes wear, the slack in the sys- A Another feature isa reservoir for a reserve 10 tem becomes greater and therefore greaterpedal supply of liquid provided with concentric pistons, travel isrequired to move the shoes into contact at least one of which is actedon by Vacuum 01' with the drum. inasmuch as the amount of other fluidpower and another of which acts on pedal travel is limited by thespaceavailable in the operating liquid t0 force it to the master cylthe carand by the distance which the operators inder, so that the reservoirserves both for con- 15 leg may move comfortably, and inasmuch as ittaining a reserve supply of liquid and also as a is necessary to allowfor slack take-up, for suflislack take up DoWer device cient clearanceto prevent the brakes from drag- Further features are the Combination ofpower ging, for distortion of the parts due to pressure, actuation ofthe low pressure phase of a two n for drum expansion from heat, and forlining phase hydraulo SYStem and manual Operation 0f wear; therefore theleverage ratio between the the high pressure phase at high ratios; anannu' pedal movement and the movement of the shoes lar plunger for themaster Cylinder Surrounding is limited and the available mechanicaladvanl a central high pressure plunger and normally tage is alsolimited. operated separately by power in combination We have discoveredthat if the shoes be autowith means onthe central plunger for operating5 matically moved into contact with the drum the annular piston in anemergency; the arwhenever lt is desired to apply the brakes andrangement of check valves in the reservoir; ccnthen the pedal used onlyto apply greater prestrol of the power operation electrically; and aSure, and to take care 0f drum expansion due to pressure relief cylinderhaving connections leadheat, little reserve of pedal travel need bereing from both ends thereof and provided with a 30 tained and also themovement of the pedal rela- Spring urged piston therein tive to thesmall movement of the shoes can be Further objects and features of theinvention relatively large. Therefore, it is possible to use will beapparent after a reading of the suba large leverage ratio and obtainhigh braking joined specification and claims and after considpressureswith low pedal pressures and at; the eration of the accompanyingdrawings in which: 35 same time, due to the fact that the power deviceFigure 1 1S a diagrammatic View in elevation 0f does not do the actualbraking, it is possible to a braking SYStem Constructed aCCoidng to ourretain a deflnite proportionate ratio between the invention; pedal andbrake so that the brake 1s perfectly Figure 2 is a view in verticalsection and on a controllable. Moreover, the effort required torelatively large scale of the combined power cyl- 40 move the shoes intocontact with the drum is indeI' and reservoir Shown in Figure 11relatively small and therefore does not require Figure 3 is a view invertical section and also the expenditure of much power. on a relativelylarge scale of the pressure relief One of the objects of our inventionis the elimchamber shown in Figure 1;- ination of the necessity ofadjustments to brakes Figure 4 ls a vlew 1n vertlcal section and also 45for wear, the pedal travel for braking remain- 0n a relatively largescale of the master cylinder ing the same throughout the life of thevehicle shown in Figure 1 regardless of wear. Figure 5 is a diagrammaticview in elevation A further object is to provide means for applyof amodied form of braking system constructed lng the brakes to the drumsautomatically thus according to our invention;

eliminating part of the pedal travel usually re- Figure 6 is a view invertical section and on an quired whereby it is possible to utilizepractically enlarged scale showing the master cylinder ilthe full pedaltravel for creating high braking lustrated diagrammatically in Figure 5;pressures. Figure 7 is a view in vertical section and on a. A furtherobject ls the provision of means restill further enlarged scale showinga modified 55 shown in Figures to their associated drums.

form of valve arrangement adapted for use in the combined reservoir andpower actuator 1 and 5;

Figure 8 is a similar view showing another -modified form of valvearrangement;

Figure 9 is a view in-vertical section showing a modified form ofreservoir;

Figure 10 ls a diagrammatic view with parts in vertical section ofanother braking system; and

Figure 1l is a view partly in elevation and partly in section showing acombined reservoir and power actuator equipped with a cover plate suchas that shown in Figure 8.

Referring in detail cially to Figures l to 4, inclusive, thereof, wehave shown diagrammatically an automobile having a frame I2, and anengine I4 and'supported by road wheels such as I6. Each road wheel isprovided with means 'for' ,drum such as I8, a backing plate such as 28and brake shoes such as at 26 and 28. The shoes are adapted to. be heldnormallyin a released position by a return spring Means are provided forapplying the brake shoes .the shoes 22 and 24 is an operating or wheelcylinder 36 to which liquid or other suitable fluid is supplied througha conduit 38 from a mastercylinder 48. Ordinarily the high pressurepiston of the master cylinder 48 is operated by a foot pedal 42 througha piston rod'44 and the low pressure piston thereof through a powertake-up device later to be described.

Fluid is supplied to the master cylinder 48 from a`combined reservoirand power slack take-up device 46 through conduits 48, 58, 5|, and 52and through pressure relief cylinder 54 in a manner which will later bemorefully described. In the process of creating power, air is withdrawnfrom the reservoir 46 by pipe connections 55 and 56, the latter havingone end leading to the intake manifold 58 of the engine I4 and having avac-v uum control valve 68 interposed between the connections 55 ,and56.

The valve 68 is controlled by a tension element 62 so that the valve isnormally open to the atmosphere but initial movement of the pedal 42moves the valve 68 to connect the pipe connections 55 and 56 and towithdraw air fromthe reservoir and power slack take-up device, 46.Interposed in the tension element 62 is a spring 64 which allowsovertravel of the pedal after the valve has connected the pipeconnections 55 and` 55.

The combined reservoir and power slack takeup device 46 compriseschiefly a main casting 66, upper cap 18, a hydraulic plunger 12, a lightcylinder or can 14 interposed between the casting 66 and the upper cap10 and a vacuum piston 16 secured to the plunger 12 in the 4can 14.Bolts 18 are provided for clamping the can 14 between the outer parts ofthe device. Annular sealing cups 88, 82, and 84 are secured in thecasting 66 around the plunger 12. Betweeny the cups 88 and 82 thecasting 66 is provided with vent openings 86 to prevent the vacuumformed at times in the can 14 from drawing liquid fromr the lower partof the casting 66. An annular plate formed with grooves 81 is securedbetween the casting 66 and the cap 68 and aids in maintaining the cup 84in position. The lower end of the plunger 12 is formed with grooves 88which -.cooperate with the grooves 81 to allow liquid to ow between thecap 68 and the lower part of the to the drawings and espenected with theconduit 4 braking the vehicle including a as 22 and 24 pivotallyanchored Positioned betweenl ao'rasoo I 92 to which the conduit 58 isconnected. The

lower cap 68 is also adapted to hold liquid which is at timesl placedunder pressure by the plunger 12, and is provided with a tapped opening84 con- 'I'he first slight movement of the pedal acts to withdraw airfrom the can 14 to pull the piston 16 downward and through it to forcethe plunger 1.2 downward. The pipe 55 is connected to the interior ofthe can 14 through a tapped opening 86 in a flanged portion of thecasing 66. A spring 98 is positlonedin the can for maintaining. thepiston 16. and the plu ger 12 normally in their upper positions.

The pressure relief chamber 54 is formed with an opening |82 positionedat one end of the chamber and connected with conduit 5| with an opening|84 positioned at the same end of the chamber and connected with theconduit 58; and with an opening |86 positioned at the opposite end ofthe cylinder and connected with the conduit 52.

lower part of the casting 88,. the casting being provided with a tappedopening Within the chamber 54 is a plunger |88 which sepl arates theopening |86 from which does not separate the opening |82 from theopening |84. The plunger |88 is provided with an annular cup valve I8which prevnts passage of fluid from the opening |88 toward the opening|84 but allows substantially free passage of fluid from the opening |84|86. Y

'I'he plunger |88 is resiiiently urged toward the end of the cylinderadjacent the opening |86 by a spring ||2 resting at its opposite endupon an adjustable seat ||4'. However, when fluid in the conduit 52 isplaced under sufficient pressure, the plunger |88 may be moved inward(toward the right as seen in Figure 3) thus compressing the head |28, acentral cylindrical plunger |22 and an annular, plunger |24 surroundingthe plunger |22. The casting ||6 is formed with openings |26, |28, and|38 connected respectively with the conduits 88, 5|, and 52 and the cap||8 is formed with an opening |32 connected with the conduit 38. Theopenings |28, |38, and |32 are relatively large but the opening |28 isrelatively small and adapted to be closed b'y the annular piston |24 asit moves forward.

The head |28 isprovided with an annular cup valve |34 allowingsubstantially free passage of fluid forward past -the passage of fluidrearwardly during the operation of the braking system. The annularplunger |24 is provided with a pair of annular cups |36 and |38, onefacing in each direction andcoacting to prevent the passage of fluid inAeither direction past the plunger. der vis another 'annular cup |48preventing the leakage of fluid from the rear of the cylinder. TheplungerV |22 adjacent to its forward end is formed with ports |42through which liquid may flow in either direction past the cup |34" toor from grooves formed in the head |28, but only the opening |84 but Atthe rear end of the cylin toward the opening head but preventing thewhen the plunger is in its normal rearward position as shown.

It is to be understood that normally the annular plunger |24 is operatedby fluid pressure introduced into the cylinder H6 rearward of theplunger |24 through the conduit 43. However, a safety feature isprovided to operate in the event of power failure. The plunger |22 justrearward of the plunger i2@ is formed with a shoulder |44 designed tocontact with a collar |46 thus serving in any emergency which might becaused by the failure of the power operation to transmit force appliedto the plunger |22 by the pedal through the shoulder and collar to theannular plunger 624.

In the operation of the device illustrated a slight pressure on thepedal 42, rst moves the port |42 to a closed position and shifts thevalve 63 so that the manifold 53 draws air from the reservoir 43 thusdrawing down the plunger i2 and forcing additional liquid under pressurethrough the conduit 48 to the rear of the cylinder 43. This liquid underpressure acts on the piston E34 forcing it forward, cutting off the port|23, and forcing the liquid trapped in the cylinder 4|] ahead of thepiston |24 past the head |20 and through the conduit 38 to the wheelcylinders 33.V

This forces the shoes outward against the drums. The spring i |2 is soweighted and adjusted that as soon as a predetermined pressure slightlygreater than that necessary to apply the brakes lightly is reached, thespring i|2 begins to compress and no further liquid is forced forwardpast the cup |34. However, the liquid already forced forward past thecup cannot return and by reason of the small area of the plunger |22additional pressure on the foot pedal is effective to applysubstantially as great pressures as may be desired. Preferably the brakeapplication by means of the power slack take-up does not cause anyretarding force to drum rotation but as a practical matter theweight ofthe spring may be adjusted so as to exert a slight retarding force only.

When the pedal is released the plunger |22 returns, thus decreasing thepressure in the cylinders 36. As soon as the plunger reaches theposition shown the valve 6U is shifted back to its normal position andair is allowed to enter the can 'i4 beneath the piston 16. The piston 16and the plunger 'i2 rise and pressure of liquid ahead of the plunger |24returns said plunger to the position shown. This allows the spring ||2to return the plunger |38 to the position shown.

Thereupon the liquid throughout the system is again reduced toatmospheric pressure. The liquid in the plunger l2 is in communicationwith the atmosphere through vents in the cap 1U; that in the conduit isin communication with the interior of the plunger 12 through the ports30 and the opening 92; that in the right hand side of the chamber 54 isin communication with the v conduit 53 through the openingl |04; that inthe cylinder 43 ahead of the plunger |24 but rearward of the head |23 isin communication with the said right hand side of the chamberl 54through the conduit 5| and the port |28; that in the left hand side ofthe chamber 54 is in communication with the said last named portion ofthe cylinder 4|! through the conduit 52; that in the forward portion ofthe cylinder 40 is in communication with the portion just rearward ofthe head |20 through the port |42 and the grooves in the head |20; andthat in the rearward portion of the cylinder is in communication withthe in terior of the plunger 12 through the conduit 4B,

the cap 68, the grooves 8l and 89, and the ports 93. Thus the entiresystem is automatically adjusted to compensate for expansion orcontraction vof the liquid due to temperature changes, for any wastagewhich might occur in operation,

and for the liquid trapped ahead of the plunger connected through theconduit 256, the valve 233.

and the conduit 254 with the power actuator and reservoir 243, thelatter being similar in all respects to the unit 43. The pressure outletof the unit 246 is connected by a conduit 243 with the inlet 323 of themaster cylinder 233 and the reservoir outletof the unit 2li@ isconnected by a conduit 250 with a small cup 32? ,cn said master cylinder24U. The master cylinder 243 is proyvided with an outlet conduit 233leading to wheel cylinders (not shown) and is operated by a pedal 242through piston rod 244 and through the valve 263.

The pedal 242 is adapted to operate valve 233 electrically. To` thisend, the pedal 242 is formed with an extension 350 adapted when thepedal is rst moved to close a switch 352 interposed in circuit with abattery 354 and a solenoid 356, the latter being connected to operatethe valve 266.

The cylinder 24|] is formed of a main cylindrical casting 3|6 and aforward cap 3i3. It is provided with fixed head 320, a central piston322 and an annular piston 324. A port 323 is provided connecting the cup32? with the interior of the cylinder just ahead of the rearwardposition of the piston 324 and a port 342 is provided in the forward endof the plunger 322.

Means are provided Within the cylinder itself which perform the functionof the pressure relief chamber 54. A`shou1der 344 formed on the plunger322 cooperates with a collar 346 in a manner similar to that describedabove in connection with shoulder |44 and collar |36. The collar 346 ismaintained in contact with an annular cup 338 by a suitable spring. Thecup 333 is associated with an annular head 353 to which there isconnected a valve cage 360 housing a relatively heavy spring 3|2.` Therear end of the spring 3|2 bears on the head 353 and the forward end ona collar 362 which in turn bears on the rear end of an extension 364formed on the piston 324. The chamber formed between the heads orpistons 324 and 358 is connected to the reservoir through an opening 363leading into the cup 323.

The operation o-f the system disclosed in Figures 5 and 6 issubstantially the same as that described above in detail in reference toFigures 1 to 4 inclusive. However, the initial movement of the pedal 242closes the switch 352 which is preferably la snap switch and thiscompletes the electric circuit and operates the solenoid 356 and throughit the valve 260. Fluid under pressure forced down by the actuator 246through the conduit 248 to the cylinder 24U actson the cup 338 and theforce thereof is initially transmitted through the head 358, the spring3|2, the collar 362, and the projection 364 to the piston 824. However,as soon as the pressure in the system reaches the predetermined minimum,the spring 8.12 begins to compress and further movement of the pedalacts through the small diameter piston or plunger 822. Should the vacuumfail due to failure oi' the motor, the pressure from the pedal 242 istransmitted through the rod 244 to the plunger 322 and through theshoulder 844 thereon to the collar 346, the cup 338, the head 858 to thespring 312 and thence to the piston 324.

In Figures 7 and 8 are shown caps 410 and 510 which may be substitutedi! desired for the cap 10 shown in Figure 2 or for; the cap of thereservoir 246. The cap 418 is provided with a one way check valve freeingress of air but prevents the escape thereof. -It is also providedwith a spring loaded valve 414 comprising a cup 416 and a spring 418.the spring being of predetermined tension. By means of the arrangementthe liquid in the reservoir and therefore throughout the system ismaintained under a pressure slightly more than atmospherio. In Figurel'l is shown the cap 518 substituted for the cap 10 as a cover for thelreservoir 46.

' 'I'he cap 510 is provided with a two way valve 514 comprising a flap516 acted on by a spring 518 and formed with ports 588. 'I'he flap 516also carries a check valve 582, provided with a stem 584, the valve 582being maintained closed to outward passage by a spring 586 but allowing`substantially free inward passage of air.

Ii' the pressure in the system reaches a value greater than desired, thespring 418 or 518 compresses, the cup 416 or the flap 516 lifts from itsseat and air is allowed to escape. On account of th`e free inwardpassage of air and the pumping action of the plunger 12, thepredetermined pressure is soon built up and maintained.

In Figure 9 is shown a combined reservoir and power cylinder646 providedwith a piston 616,

and a bellows 612 adapted to be collapsed when air is withdrawn by theintake manifold from beneath the piston 616 out through the opening'I'hus liquid may be forced out through the` opening 684 into conduit648 to the master cylinder associated therewith.A A check valve 611 maybe associated with the piston 616 to allow 4the system to be replenishedwith liquid when necessary.

In Figure 10 there is shown a vacuum booster 146 connected throughconduit 155 with conopening 82 of the trol valve 168, the valve beingconnected through conduit 156 with the intake manifold 158. 'I'hecontrol valve 168 is operated by the pedal 142 through a tension link162 in which there is interposed a spring 164. The pedal is connectedthrough a link 143 and a piston rod 144 with a master cylinder 148, thelatter having its outlet connected to a conduit 138 leading to a wheelcylinder 136 positioned in 'a brake drum 118.

The master cylinder 148 is provided with a` plunger 822 which at itsrearward end is provided with a pair of reversed sealing cups 838 and84| and at its forward end extends through an annular head 820 and anannular packing cup 834 associatedwith said head. Just rearwardly of thehead 820 the` cylinder is formed with a recess 82| which is connectedthrough a conduit 148 with the booster'cylinder 146. It is to be notedthat the booster cylinder 146 is not formed with an openingcorrespondingto the booster cylinder 46, all of the 412 which allows substantiallyliquid being supplied through the one conduit 148. I'he cylinder 146 isexactly like the cylinder 48 except for the- 82 and serves as areservoir as well as a booster. sponding to the grooves 81 and 88 allowcompensation.

In the operation of this embodiment of our invention depression oi'thepedal 142 moves the port 842 ahead of the cup 834 and operates thevalve 160. motor operates the booster cylinder 146 to force fluidthrough the conduit 144 past the head 828 and the cup'834 and throughthe cylinders 144, thus moving the shoes to the drums. Thereafterfurther pressure ot the pedal 142 moves the plunger 822 further forwardincreasing the pressure in the wheel cylinders and applying the shoes tothe drums with greater force;

It is to be understood] that the above described embodiments of ourinvention are forthe purpose 'Ihereupon suction created by' the' Groovescorrethe conduit 188 to of illustration only and various changes may be'made therein without departing -from the spirit and scope of theinvention.

We claim: j 1. In a hydraulic force transmission system, a mastercylinder, a piston in said cylinder provided with a packing allowingpassage oi' iluid past said A ing said piston to apply greater pressuresto the 2. In a hydraulic brake system, a brake pedal, A

a master cylinder, a wheel cylinder, lines connecting said mastercylinder and said wheel cylinder, a power slack take-up device includinga piston in said master cylinder operated by initial movement of thebrake pedal and acting on the liquid to produce pressure in the linessuicient to take up the shoe clearance, a second piston in the mastercylinder operated by further movement of the pedal which after the slacktake-up will produce braking pressures in the lines without assistancefrom the power device and means for preventing said braking pressurefrom reacting on said power slack take-up piston.

3. In a hydraulic force transmission system, a master cylinder, powermeans including a piston arranged to impose pressure on Athe liquid anda pneumatically actuated piston arranged to operate the liquid pistonfor forcing a relatively large quantity of liquid through from themaster cylinder to take up initial clearances, another piston forforcing additional-liquid from the cylinder to develop higher pressuresand means for preventing said higher pressures from reacting on theilrst mentioned piston and on the pneumatically actuated piston.

4. Inga hydraulic brake system, a master cylinder, power means includinga power operated piston for forcing a relatively large quantity of fluidfrom the master cylinder to take up brake clearances, a piston forforcing additional uid from the cylinder to develop higher brakingpressures, and means to insure operation of the power operated pistonmanually in the event of failure of power to operate said piston. i

5. In'a hydraulic force transmission system a master.. cylinder, Aavacuum cylinder having connecti'ns leading to said master cylinder, afluid motor connected to said master cylinder, and a ed in said mastercylinder, an annular pistonv mounted in said master cylinder andsurroundfing said central. piston, means for displacing one l of saidpistons, separate means for displacing the other of said pistons, andmeans associated with one of said pistons for bearing 'upon anddisplacing the other said piston in the event of a failure of one ofsaid displacing means.

8. For use in a hydraulic force transmission system a master cylinder, acentral piston mounted in said master cylinder, an annular pistonmounted in said master cylinder and surrounding said central piston,manual means for displacing one of said pistons, power means fordisplacing the other of said pistons, and electric means for controllingthe operation of said power means.

9. In a hydraulic force transmission system a reservoir formed of acontainer having two diameters, an annular disk slidably mounted in saidcontainer and having a cylindrical extension, means for drawing air fromsaid container beneath said disk, means for venting air from saidcontainer above said disk. means for filling the cylindrical extensionwith liquid, an inwardly opening check valve positioned above said disk,and an outwardly opening spring loaded check val-ve also positionedabove said disk. 40 l0. n a hydraulic force transmission system areservoir formed of a container having two diameters, an annular diskslidably mounted in said container and having a cylindrical extension,means for drawing air from said container beneath said disk, means forventing air from said container above said disk, means for lling thecylindrical extension with liquid, and a check valve opening freely inone direction but spring loaded in the opposite direction secured tosaid container above said disk.

ll. For use in a vehicle, means for retarding said vehicle, a powermeans having a variable stroke for operating said retarding means with apressure so light that it need. not be graduated, relatively powerfulmanually controlled applying means for adding a graduated pressure, andmeans comprising a check valve for preventing the graduated pressureadded by the manually controlled applying means from reacting on therelatively light power means.

l2. In a force transmission system using iluid, an operating cylinder, amaster cylinder, connections between said cylinders, a reservoir, aconnection between said reservoir and said master cylinder, a pair ofpistons in said master cylinder having diierent areas, means includingsaid pistons for dividing said master cylinder into a plurality ofcompartments including a compartment in which the uid is acted on bysaid vlarge area piston and a compartment in which the fluid is acted onby said small area piston, a pressure relief chamber connected to saidfirst mentioned compartment, means for bypassing iiuid from said firstmentioned compartment to said last mentioned compartment and fortrapping the fluid thus bypassed, means for operating said large areapiston, and separate means for operating said small area piston.

13. A hydraulic force transmission system comprising a master cylinder,an annular head in saidmaster cylinder, a packing cup associated withsaid head and serving as a one-way check valvea piston sliding throughsaid head and cup, a manually controlled pedal connected to said piston,and means for forcing liquid into said cylinder Yand past saidcup'including a power motor having a variable stroke for operating saidretarding means with a pressure so light that it need not be graduatedby the initial movement of said pedal.

14. For use with a hydraulic force transmission system, in combination acontainer formed with a pair of cylindrical portions one having a largerdiameter than the other and each having a vertical axis aligned with theaxis of the other, a piston in said container formed of an annular diskhaving an external diameter corresponding to the diameter of the largercylindrical portion and provided with a circular opening having aninternal diameter corresponding to the diameter of the smallercylindrical portion, and a cylinder having an external diametercorresponding to the diameter yof the smaller cylindrical portionsecured to the disk and extending through and closing the openingtherein, said cylinder'having its lower end closed and its upper endopen whereby it serves not only as a piston but also as a reservoir fora reserve supply of actuating fluid.

l5' A slack take-up and force-ratio multiplier for hydraulic brakes andthe like, comprising in combinatiorna displacing piston for taking upslack; a displacing piston for exerting braking force; power means foractuating the first piston; manually actuated means for actuating thesecond piston; controlling means for said power means arranged to beoperated upon initial motion of said manually actuated means in aforcedeveloping direction; and connections whereby said manuallyactuated means will also actuate the rst piston should said power meansfail to function.

16. A slack take-up and force-ratio multiplier for hydraulic brakes andthe like, comprising in combination, a displacing piston for taking upslack; a displacing piston for exerting braking force; power means foractuating the first piston; `manually actuated means for actuating thesecond piston; controlling means for said powerv means arranged to beoperated upon initial motion of said manually actuated means in aforcedeveloping direction; and connections between said pistons wherebymotion of the second entails motion of the rst, should said power meansfail to function. f

17. The combination of claim 16, further characterized in that one ofsaid pistons is arranged for'limited sliding movement in the other.

18. A slack take-up and force ratio multiplier for hydraulic brakes andthe like, comprising in combination, a displacing piston for taking upslack; a displacing piston for exerting braking force, said pistonsbeing in such one-way thrust relation with each other that motion of thesecond in a displacing direction entails motion of Y the first in a,displacing direction; power actuating means in one-way thrust relationwith the rst piston and capable of moving it in displac- 10 tween therst piston and ing direction; manual actuating means for the secondpiston; and a controller for said power means arranged to-be shiftedupon initial motion of said manual means in a displacing direction.

19. The combination of claim 18, further characterized in that one ofsaid pistons is arranged tor limited sliding motion in the other.

20. 'Ihe combination of claim 18, further characterized in that theoperating connection beits power actuating 'i ovanoo means is arrangedto lock against retrograde motion oi' the piston at the limit of itsdisplacing motion and thus protect the power means from braking stress.

21. The combination of claim 16 further char# acterized in that thesecond of said pistons is arranged for Jimited 'sliding movement in therst.

EUGENE G. CARROLL. ROY B. SANFORD.

